1. Field of the Invention
The present invention relates to a generating system including a generator having a permanent magnet disposed in the magnetic field.
2. Description of the Related Art
As a magnetic field control system of a vehicular generator, field current control technology for controlling the output power of a generator is well known. JPA 58-66538 proposes to reduce engine loads by controlling the field current for a limited time after the engine starts and the generator output voltage is generated. JPB2-6-38720 proposes to reduce the engine loads by controlling the field current to a limited value while the generator is still cool.
A vehicular generator having both permanent magnets and field coil is also well-known. For example, a permanent magnet generator which is composed of a magnetic core having a plurality of claw poles and a plurality of permanent magnets disposed between the adjacent claw poles is proposed to increase the magnetic flux interlinking the armature coils. A tandem-type generator which is composed of a rotor having field coil and a rotor having permanent magnets is also proposed. A field-coil-permanent-magnet-combined generator, in which the field coil is energized in the direction to offset the magnetic field of the permanent magnets in order to reduce the iron loss and the engine load, is also proposed in JPA 6-217411.
A vehicular generator provided with permanent magnets for supplying the magnetic field without a field coil (or permanent magnet generator) is also well-known.
In the above mentioned permanent magnet generator and field-coil-permanent-magnet-combined generators, the magnetic field (or outside magnetic field) generated by the armature coil or the field coil is apt to demagnetize the permanent magnet. That is, when the output current or the field current increases, the outside magnetic field strength may increase to an amount to irreversibly demagnetize the permanent magnet, thereby reducing the output power of the generator.